Piston Pin matterial

[borna]

Hello all,
I got this Chinese multi-cylinder engine, and during the assembly, I noticed that I am missing one piston pin. This is a picture of one set of piston, pin, and connecting rod. Since I decided not to wait for them to send me a piston pin, I’m planning to make my own. That said, the piston is aluminum, and the connecting rod is most likely brass or bronze. So, my question is: What material is best for making the piston pin? Can I use HSS? Should it be hardened or not? If HSS is not a good metal for it, please let me know what to use?

Thanks

 

[kuhncw]

You could use either a piece cut from a drill blank (HSS) or you could use drill rod or silver steel depending on what it is called in your area. Either water or oil hardening are ok and no need to harden the drill rod in this application.

Please let us know how this turns out and post a picture of your engine.

Regards.

Chuck

 

[borna]

You could use either a piece cut from a drill blank (HSS) or you could use drill rod or silver steel depending on what it is called in your area. Either water or oil hardening are ok and no need to harden the drill rod in this application.

Please let us know how this turns out and post a picture of your engine.

Regards.

Chuck

Thanks for the info. Since the diameter of the pin is 4mm exactly, this should work?
https://www.amazon.com/dp/B07SYYDTVZ/ref=ox_ya_os_product?th=1

 

[kuhncw]

That should work. A drill blank would cost less.

Chuck

 

[abby]

Quick question , why would you not harden the piston pin made from drill rod?

 

[kuhncw]

It is ok to harden the piston pin and necessary in full scale engines. Loads are light in our model engines and the engines usually don't run hundreds of hours. Again, either method is ok. Builder's choice.

Chuck

 

[rleete]

Even plain CRS is harder than the rod, so hardening would not be necessary.

 

[petertha]

Hardened dowel type pin should be fine, just check the tolerances. Some are +/- either side of nominal dimension depending on the application, some are plus & some are minus. Presumably the ends are 'plain' meaning no end features like a hole for softer scuff pads? If so, then if the stock has to be machined, hardened would present a few more challenges.

 

[Steamchick]

Even regular Mild steel is adequate for this application. Steel and Bronze are similar densities so balance should not be a significant problem.
BUT if you can get some hard brass or bronze that should be exactly the same mass as the Chinese pin.
However, (1) why not ask the supplier for a piston pin? (2) If that fails, "shout" at the supplier, saying you will give them a bad report on the web unless they finish the contract of delivering ALL the parts? - I have only had to do that once, but bad reports on the internet can really upset the Orientals, so they are quick to resolve issues in that case.
On models, some people are not concerned if the model shakes a bit. But this engine should be relatively smooth, and may be spoiled by using a steel pin instead of a Bronze pin. - You can only try that and see?
K2

 

[stevehuckss396]

I agree with Chuck. Hardened drill blanks work great.

 

[abby]

The original question was " can I use HSS , should it be hardened or not ?"
Answers then went on to refer to drill rod and drill blanks.
For us in the UK, what are drill rods and what are drill blanks ?
From past experience I believe that US drill rod is what in the UK we call silver steel , a carbon steel which can be easily hardened and tempered to whatever requirement.
However drill blank ? I presume this to mean use the shank (chuck end) of a HSS drill , as I am sure we all know , the shank of HSS twist drills and end mills are not hardened , infact larger sizes often have welded steel shanks.
So , having worked in the Clarkson International factory , I ask how do you harden HSS ?
Although I did not work in the hardening shop I know it was a complicated process involving molten salts of sodium cyanide and Barium at very high temperatures and probably not the sort of thing to do at home.
Dan.

 

[Richard Hed]

The original question was " can I use HSS , should it be hardened or not ?"
Answers then went on to refer to drill rod and drill blanks.
For us in the UK, what are drill rods and what are drill blanks ?
From past experience I believe that US drill rod is what in the UK we call silver steel , a carbon steel which can be easily hardened and tempered to whatever requirement.
However drill blank ? I presume this to mean use the shank (chuck end) of a HSS drill , as I am sure we all know , the shank of HSS twist drills and end mills are not hardened , infact larger sizes often have welded steel shanks.
So , having worked in the Clarkson International factory , I ask how do you harden HSS ?
Although I did not work in the hardening shop I know it was a complicated process involving molten salts of sodium cyanide and Barium at very high temperatures and probably not the sort of thing to do at home.
Dan.

You can buy silver steel (drill rod--You Brits really need to learn English!) that has not been made into drills--it is "blank" thus drill blanks. I use it for different things. You should be able to get it cheaply.

Me thimpfks it would be a mistake to use HSS for your purpose.

 

[Jasonb]

As Said silver steel is drill rod a carbon steel that is accurate on size and what I use

A bit of 4mm mild steel is likely to come in undersize so not good for this application unless you like a knocking engine though you could turn down a larger diameter

Drill blanks are just lengths of HSS rod much like buying a round HSS toolbit. Fully hardened and ground all over Also they ar eonsize whereas the shank of a drill bit is often a little undersize.

https://www.cromwell.co.uk/shop/cut...ss-hardened-groun-d-drill-blank/p/SHR0242424J

 

[Bentwings]

Even plain CRS is harder than the rod, so hardening would not be necessary.

Have to disagree . Top fuel wrist bins are super hard. They have even gotten thicker over the years. Unless you run a lot of nitro model engines don’t need to go much beyond dowel pins unless you have something a standard dowel pin won’t fit. If you run a bejillion rpm standard dowel pins work fine rods pistons and crank will fail first.

 

[Steamchick]

Agree. Piston pins are often a very high quality steel, but in "everyday" cars can be cheap steel, precision ground and surface hardened.
While I audited piston and ring manufacturing, piston pins (gudgeon pins in PROPER English) were not audited by me. They were weighed individually to within 1mg, as we're all piston sub components, and the set of parts coded for weigh and fits, and graded for matching balance and fit to each bore, small con-rod end, and Piston to pin. As were crank journals bearing shells and housings. Assembly to graded parts was only possible with very high production volumes, but permitted clearances to be maintained to tolerances that were a fraction of the machining capability.
Piston pins were forged, then ground and induction hardened. Not a parallel bore but tapering in to the middle. Not seen on models?
K2

 

[abby]

Richard Hed we Brits do not need to learn English ,but Me thimpfks you might. Drills are made of HSS , that's high speed steel in any language.
Silver steel, what you call drill rod is not HSS , and it is not and never was made into drills commercially.
I , like most model engineers , have a large stock of silver steel which I often use to make D-bits and counter bores. I use it for axles and pins of all descriptions both in the hardened state and in the as supplied condition.
The point I was trying to make is the reference to hardening HSS ,Me thimpfks you can't do it in your shed !
Dan.

 

[mrehmus]

Quick question , why would you not harden the piston pin made from drill rod?

Not needed. The engines are not run long enough to consider wear in the area. The metals it interacts with are fairly good bearing material.

 

[Bentwings]

Agree. Piston pins are often a very high quality steel, but in "everyday" cars can be cheap steel, precision ground and surface hardened.
While I audited piston and ring manufacturing, piston pins (gudgeon pins in PROPER English) were not audited by me. They were weighed individually to within 1mg, as we're all piston sub components, and the set of parts coded for weigh and fits, and graded for matching balance and fit to each bore, small con-rod end, and Piston to pin. As were crank journals bearing shells and housings. Assembly to graded parts was only possible with very high production volumes, but permitted clearances to be maintained to tolerances that were a fraction of the machining capability.
Piston pins were forged, then ground and induction hardened. Not a parallel bore but tapering in to the middle. Not seen on models?
K2ive done cylinder honing on Sunnen hones and fully automated truck diesel engine Hines. Almost always itvwas a thre stage or step process. The first the cylinder is bores about .003” under size first home takes about 3/4 of the excess out. Leaving perfectly straight surface with cross hatch, second stage is sizing which looked the same cross hatch but slightly different included angle. This is near finished size maybe .00.5” the final stage is the plateau and final size this is less than 1/2 thousandth it puts the final smooth cross hatch . In the processes there is no taper of any kind permitted. I forgehat the RA number is but you can’t feel it on a finger nail. On the automated line I saw ten hour shifts with no cylinder rejects one 8 cyl V 8 block per minute sizes were measured with air gages extremel accuracy. No lapping was ever done. Lapping you almost always get taper or bell mouth you can get small bore Hines for not a lot of cash forget brake cyl hones they should require a license like easy outs to even purchase let alone use. Like gun control LOL I made a good living fixing tapered bores and removing broken easy outs. You need a good bore gage it will be more expensive than the hone I’ve seen some really Raghu bores. Our top fuel engines some times had double rings after burning pistons. Early aluminum pistons were eeldsblr aluminum so burned areas could be machined and welded. Not practical now $ 3000a piston plus rings 8 per run. Throw them in the scrap slum barrel.

 

[Steamchick]

As hardening steel is a heating process, it can be achieved in many ways from heating, various flames, coke hearth fires,, or "barbecues", induction heating, etc.
A front wheel stub axle forging had the bearing inner-track part of the axle induction hardened and cooled by an air blast. The induction heating raised the temperature to just the right value, and the air-quenching cooled it at the right rate. Change the induction heating current or time, or the air-quench time, and the bearing inner track would be at the wrong hardness leading to early life failures - or stub axle breakage!
A bit of "high technology" unnecessary for a Chinese model engine I think?
I should heat a Gudgeon-pin (piston-pin for the Yanky Doodle Dandies) to a dull red, quench in oil, polish to shiny metal then heat until yellow temper lines appear and just start to change to blue, then quench in water. A final polish and the pin should be adequately hardened and tempered. The change point from yellow to blue colour is related to the reflected wavelength of light as smaller crystal structures are created at the surface of the steel at particular temperatures. But not so small as to create embrittlement, yet also retain pin-core ductility.
Easy to do and hopefully you'll never find out if you got it wrong!
N.B. Gudgeon pins were used on many linkages, eg. Con-rod to cross-head to piston-rod pins - as common on Double acting pistons - which later became a position inside the piston, when the cross-head was combined with the piston as the piston skirt on single acting pistons. So folk who didn't know the correct engineering term just called them "piston pins" and the name became common parlance in American Motor Industry parlance. (The Great Henry Ford's mob?). Just odd how the Trunk - at the front of an Elephant - became a storage compartment at the rear of motor cars? (Perhaps more polite than referring to that same storage compartment for luggage as "the Rectum"? - That may conflict with the the idea of "putting the a##ehole in the driver's seat"?- I wonder at how words are mis-used and become common parlance as generation evolve the language. I struggle with Mobile phone and computer terminology too... (Media is plural of a Medium, to me. But "a Medium" is someone who "sees" things in their own mind, attributed to ghosts or spirits or whatever unknown invisible messaging service - so we call the News programme on TV "the media"... I.E. as believable as Ghosts and spirit messages? ).
K2

 

[Richard Hed]

Richard Hed we Brits do not need to learn English ,but Me thimpfks you might. Drills are made of HSS , that's high speed steel in any language.
Silver steel, what you call drill rod is not HSS , and it is not and never was made into drills commercially.
I , like most model engineers , have a large stock of silver steel which I often use to make D-bits and counter bores. I use it for axles and pins of all descriptions both in the hardened state and in the as supplied condition.
The point I was trying to make is the reference to hardening HSS ,Me thimpfks you can't do it in your shed !
Dan.

When in the Philippines, I have several Brit friends and when there is a word difference between us, I always say that" YOu Brits need to learn English". some non-English speakers might not get the joke.

I do have to admit, when speaking of HSS, I was thimpfking of cobalt steel for tool bits. My mistake. And thanks for pointing out that silver steel is NOT exactly the same thing as drill rod. I thot they were the same. I use a bit of drill rod for this and that also.

Ken: that would be "wrist pin" as far as I know. Learn to speak American!